1. Field of the Invention
This invention relates generally to a method for automatically selecting a welding gun for a welding operation and, more particularly, to a method for estimating the geometrical parameters defining the size of a welding gun suitable for a welding operation.
2. Description of the Related Art
Welding is sometimes performed to join two parts together. There are various types of welding technique, such as electric arc welding and resistance spot welding. Resistance spot welding is the most common joining operation used in automotive assembly line. In resistance spot welding process, the welding is performed by placing the parts to be joined together between the electrodes of a weld gun and an electric current is passed through the electrodes. The parts are welded due to the high temperature caused by the resistance to electric current flow of the electrodes. In an automotive assembly line, parts are joined at various weld points with a variety of orientations during a weld operation.
In a typical vehicle, the number of weld points are several thousand. To balance work across assembly line stations, these weld points are grouped into sets of six to eight weld points each called weld operations, where a single weldgun on a single robot perform welding at weld points belonging to a single weld operation. Selection of a weld gun for a specific welding operation depends on a set of operational and geometric constraints. The process constraints depend on material stack up and the geometric constrains depend on the geometry of parts and tools/fixtures near the weld point.
Current methods of weld gun selection typically employs software (UG-NX) assisted manual process. An engineer selects weld guns iteratively based on previous experience and by taking measurements from 2-D sections manually. However, this method is time consuming and also requires manual iterations for selecting the correct weld gun. Further, the weld gun selected using this method can fail while validating the weld gun for all the weld points of a welding operation. The weld gun is validated by manually operating the selected weld gun at the weld point such that the weld gun does not interfere With the geometry of any part. Moreover, the method doesn't provide information about all the directions in which the weld gun can approach the weld point.
Another way to perform weld gun selection is to use eM-Simulate's weld gun selection capability. But that too is necessarily a validation approach rather than a selection approach. The eM-Simulate method is a brute force method of validating each of the weld guns in a library of weld guns against all of the weld operations by performing successive interference checks around the weld points. This method is time consuming and does not capture the complete solution space available for the valid weld gun sizes for a given set of weld operations.